What is the moral proposition of Blake's poem “A Poison Tree"?

Suppressed anger could lead to spiritual degeneration—this is the central moral proposition of Blake’s “A Poison Tree.” According to the poet, it’s always good to disclose one’s anger instead of suppressing it. Expression of anger doesn’t allow it grow into a malicious force. Instead, it paves the way for a better understanding and healthier relationship between two persons.

On the other hand, if one buries anger within oneself, it gets planted like a seed. With...

Suppressed anger could lead to spiritual degeneration—this is the central moral proposition of Blake’s “A Poison Tree.” According to the poet, it’s always good to disclose one’s anger instead of suppressing it. Expression of anger doesn’t allow it grow into a malicious force. Instead, it paves the way for a better understanding and healthier relationship between two persons.

On the other hand, if one buries anger within oneself, it gets planted like a seed. With time, it grows into a destructive and malicious force.

The poet has beautifully expressed this idea by using an extended simile of a seed. The seed of anger gets planted once we suppress our wrath instead of acknowledging it. Behind our fake smiles and gentle demeanor, we keep it hidden.

And I sunnéd it with smiles
And with soft deceitful wiles.

Meanwhile, the seed is nourished and grows into a big tree. Its growth suggests the gradual corruption of the mind. It means the spiteful evil thoughts grow stronger in us.

Blake stretches the simile further and says that, with time, the seed develops into a fruit-bearing tree.

And it grew both day and night,
Till it bore an apple bright,

The fruit the tree bears is highly poisonous. The enemy of the speaker dies as soon as he plucks the fruit and tastes it. We see that the suppressed anger represented by the apple has grown into a malevolent force, powerful enough to destroy a life.

So, the poet is suggesting that if wrath is suppressed, it will corrupt one’s mind and thoughts. Suppressed and buried, it will grow sinister and dangerous. Thus, one should acknowledge one’s anger immediately in order to avoid one’s spiritual degradation.